Self-lubricating anti friction bearings

ABSTRACT

Self-lubricating roller and ball bearing structures are described in which the ball or roller elements are lubricated by means of rotatable spacing inserts positioned between the balls or rollers in sliding contact therewith. The spacing inserts are made of a polymeric self-lubricating composite containing dry lubricants interspersed throughout the polymer.

United States Patent [191 Laux et a1.

[ Feb. 5, 1974 SELF-LUBRICATlNG ANTI FRICTION BEARINGS Inventors: Raymund Wilhelm Laux; Reinhold Sauer, both of c/o Dow Corning G.m.b.l-l., Munich, Germany Filed: June 15, 1972 Appl. No.: 263,324

US. Cl. 308/206 Int. Cl. Fl6c 33/00 Field of Search 308/307, 7, 206

References Cited UNITED STATES PATENTS 5/1924 Sheldon 308/206 FOREIGN PATENTS OR APPLICATIONS 1,270,201 7/1961 France 308/7 Primary Examiner-Charles J. Myhre Assistant ExaminerFrank Susko Attorney, Agent, or Firm-Howard W. Hermann [57] ABSTRACT Self-lubricating roller and ball bearing structures are described in which the ball or roller elements are lubricated by means of rotatable spacing inserts positioned between the balls or rollers in sliding contact therewith. The spacing inserts are made of a polymeric self-lubricating composite containing dry lubricants interspersed throughout the polymer.

2 Claims, 15 Drawing Figures PAIENTED 5 I974 SHEET 2 BF 4 FIG. 7

FIG. 6

PAIENTEU 74 SHEET 3 BF 4 FIG. 70

Wu: C

FIG. 9

FIG. 74

FIG. 73

FIG. 72

1 SELF-LUBRICATING ANTI FRICTION BEARINGS BACKGROUND OF THE INVENTION The invention relates to self-lubricating antifriction bearings consisting of rolling elements located between two circular tracks and which are kept apart from each other by spacing elements.

Spacing elements in antifriction bearings are usually designed in the form of so'called ball or roller cages formed from steel or brass sheet. In general, antifriction bearings have to be lubricated by oils or greases.

When antifriction bearings are subjected to large radial loads and corresponding speeds at high ambient temperatures of e.g., 200 250C, they are extremely difficult to lubricate, since even special lubricating oils and greases thend to thicken, polymerize, and carbonize at these temperatures.

Also, when used in vacuum atmospheres, as e.g., in space travel and vacuum technology, the conventional lubricants are not adequate for safe use for bearings without repeated relubrication. The same problems occur with antifriction bearings used in reactor technology, where they are subjected to radiations from radioactive materials.

Attempts have been made previously to produce selflubricating antifriction bearings by employing solid lubricants in powder form. lt has, however, become evident that the power restricts the clearance between the rolling elements and the grooved tracks resulting in the seizure of the bearings after a limited period of operation.

It is known that antifriction bearings can be lubricated by means of treating the grooved tracks of the races with a bonded lubricant coating. The treatment of bonded lubricant coating, is, however, very critical, being subject to close tolerances of film thickness, and requires complicated and therefore uneconomical processing steps, such as degreasing, chemical or mechanical roughening of the raceway surfaces, application of the coating, its curing, etc. Since the thickness of the film must not exceed a few thousands of a millimeter, the films soapplied contain only a small reservoir of lubricant so that the self-lubrication in the absence of any possibility of its regeneration is of only relatively short duration. Furthermore, the high Hertz pressures occurring between the rolling elements and the track in the bearing, particularly during the initial stages of operation, result in the displacement and consequent loss of some of the lubricating coating. To prevent seizure of the rolling elements by the displaced coating, it is necessary to provide for greater clearance between the rolling elements and the track then in the normal case of grease or oil lubricated bearings. This also adversely affects the life of the bearing as well as its running and vibration behaviour as a result of additional dynamic forces.

Finally, it is also already known to use spacing elements in the form of sliding elements made from plastic materials containing a solid lubricant such as molybdenum disulphide or graphite. The resulting wear of the sliding elements increases the clearance between the sliding elements and rolling elements to intolerable levels within a relatively short period of operation so that the use of the spacing elements in the known manner does not present a satisfactory solution.

The manufacture of ball and roller cages of antifriction bearings of polytetrafluorethylene or polyamide or other plastics materials does not result in an adequate self-lubrication effect, particularly since the ball and roller cages made of the aforesaid plastics materials are not sufficiently wear resistant, resulting in relatively short bearing life. I

SUMMARY OF THE INVENTION The primary object of the invention is to provide an antifriction bearing which retains its self-lubricating properties over a long period of operation at medium speeds, large radial loading and relatively high operating temperatures without intolerable increase in clearance between spacer rolls and rolling elements.

The invention solves this task by making the spacing elements in the form of spacing rollers which are at least partly made from lubricating bearing material which is preferably a polymeric composite having dry lubricants interspersed throughout the polymer. This results in rolling of the spacing rolls and the rolling elements against each other, so that the wear of the lubri cating spacing rollers does not exceed the amount which is absolutely necessary for lubrication of the bearing by transfer of dry lubricant to the rolling elements. When, as in a preferred form of the invention, the radius of the rolling face on the outer track, on which the lubricating spacing rollers roll, is smaller or larger than the radius of the outer race, on which the rolling elements roll, then each of the spacers rolls between two rolling elements. At the same time, the rollers are pressed against the outer running track by a force resulting from the weight, the centrifugal forces, and the tangential forces from the rolling elements. This force along with a sliding motion between the lubricating roller spacers and the bearing rolling elements resulting from radii differences, superimposed on their rotation, results in wearing off of some lubricant.

The relative motion between the lubricating rollers and rolling elements can be adjusted exactly to the extent required for lubrication of the bearing by suitable adjustment of the ratio between the radii of the rolling faces of the lubricating spacer roll and the rolling elements. A further control in lubrication can be obtained by subdividing each lubricating roll over the area with which it contacts the rolling element, axially into severa] sections, at least one of which comprises a material such as silicon carbide, which possesses greater wear resistance than the bearing material. In this embodiment of the invention the amount of bearing material being worn off does not exceed that corresponding to the wear of the section of increased wear resistance. This section can, for example, comprise one or two steel rings which are placed either between two symmetrical portions of bearing material of the lubricating spacing roll, or at its ends. These rings can be made to have a smaller diameter than the bearing materail portion of the lubricating spacer roll according to the inention, so as to be out of contact with the rolling elements. Thereby in the initial stages of running in of the hearing more lubricant can be supplied by each lubricating spacer roller, until the rolling elements come into contact with the steel rings. Thereafter the supply of lubricant is regulated by the wear of the steel rings. By varying the profile of the steel rings it is possible to increase or decrease the rate at which the lubricant is supplied by the lubricating spacer roller as the wear of the steel rings increases or decreases. ln this embodiment of the invention the supply of lubricant can thus be adjusted quite precisely to the rate at which the antifriction bearing requires lubricant. The structure together with the preferred combination of inorganic solid lubricants and fluorinated organic polymer in an organic polymer base such as epoxy resin provides a self-lubricating antifriction hearing which is economical to manufacture, requires a minimum of maintenance, and provides long life even under a large radial loads and relatively high operating temperature.

BRIEF DESCRIPTION OF DRAWINGS Further objects and attendant advantages of this invention will become obvious to those skilled in the art from the following detailed description when read in connection with the accompanying drawings wherein:

FIG. 1 is a partial cross-sectional view in elevation of a ball bearing according to the invention;

FIG. 2 is a cross-section along the line Il--Il in FIG.

FIG. 3 is a cross-section along the line IIIIII IN FIG.

FIG. 4 is an elevational view of a specimen element consisting of a metal roller with a double cone shaped constriction;

FIG. 5 is a diagrammatic view of the operational position of a lubricating roller with a smaller diameter than the diameter of the ball in a ball bearing;

FIG. 6 is a partial cross-sectional view in elevation of a roller bearing according to the invention;

FIG. 7 is a cross-section along a line VII-VII in FIG.

FIG. 8 is a cross-section through the two spacer rollers fitted in a bearing according to FIG. 6, to an enlarged scale;

FIGS. 9 to 14 show a practical example of a roller bearing according to the invention, viz:

FIG. 9 is a cross-section of the outer ring;

FIG. 10 is a cross-section of the inner ring;

FIG. 11 is an enlarged axial cross-section of a lubricating spacer roll;

FIG. 12 is a cross-section of a part of a spacer roll;

FIG. 13 is a cross-section of a metallic spacer roll;

FIG. 14 is a cross-section through the wear ring, and

FIG. 15 is a graphic depiction of a test run with a selflubricating bearing according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings, wherein like reference characters designate like or corresponding parts throughout the figures thereof, there is shown in FIGS. 1-5 a grooved ball bearing. In this bearing, eight spacer rolls consisting alternatively of lubricating spacer rolls 1 made of lubricating bearing compositions and of metal spacer rollers 2, are arranged between the bearing steel balls 3. In the grooved ball bearing shown, the number of lubricating spacer rollers l is half that of the steel balls, so that each lubricating spacer roll lubricates two steel balls simultaneously. The spacer rollers 2 may be made of steel, brass, bronze or aluminum. The contact profile of the lubricating spacer rollers l is similar to that of the steel balls 3, i.e., the curvature of the plane along which the lubricating spacer rollers are in contact with the steel balls, when viewed in their axial plane, has a radius B/2 (FIG. 3) which corresponds to the radius of the balls. This ensures mating contact of the lubricating spacer rollers with the steel balls. The metal spacer rollers, viewed in the axial direction, have a contact profile of circular curvature, (FIG. 2) or have a double conical configuration (FIG. 4). In the latter case the metal spacer rollers 2 contact the steel balls 3 only at the points e.

As may be seen from FIG. 5, the center of rotation of the steel ball bearings 3 lies on a circle around the center M of the bearing which passes through the center of the bearing balls. To effect the pressing of the spacer rolls against the contact planes of the outer circular track by the resulting pressure, it is necessary for the axis of rotation of each spacer roller to be outside the cord through the centers of the two balls, which make contact with the corresponding spacer roller, when viewed in a direction which is radial relative to the center of the bearing.

The direction of the resultant force R on the lubricating spacer roller from the axis of the roller with a line parallel to the line connecting the center of the ball bearings forms an angle 4). 4: must be positive, with the corresponding line connecting the two bearing balls adjacent this spacer rollers, i.e., the axis of the spacer roller, when viewed radially, and must not be set back towards the center of the bearing as far as the line joining the corresponding bearing ball centers but must be behind this line when viewed radially.

In the example shown in FIG. 5, the axes of the spacer rollers are also on the circle C passing through the centers of the bearing balls, the center M of which is the center of the bearing. The radius F of the contact surface of the outer running track on which the spacer rollers, i.e., the track on which the metal spacer rollers 2 and the lubricating spacer rollers 1 roll, and the radius E of the surface on which the balls run, differ from each other so that onto the rolling movement of the spacer rollers and the balls a gliding movement is superimposed, the extent of which determines the extent to which the lubricant is worn off the lubricating spacer rollers. The spacer rollers 1 and 2 are pressed by a force component K R X sine against the outer ring 6 and there roll along the points a. By suitable profiling of the edges of the ball races on either side of the track, the radius F may be made larger or smaller than the radius E, so as to obtain the desired relative displacement between ball and roller contact surface. In each case, however, it is essential to ensure the above stated condition requiring the axis of each spacer roller to be, when viewed radially from the center of the bearing, outside the line connecting the centers of those balls which are in contact with the spacer roller concerned, so that the spacer rollers are pushed against the outer track ring. When the bearing is in operation the resulting force R is generated in the unloaded zone of the bearing and is made up from the weights and the centrifugal and tangential forces of the balls and spacer rollers.

As can be seen from FIG. 3, the lubricating spacer rollers consist of two halves l and 1" between which a metal wear ring 9 is positioned. Metal rings are also provided on all front faces. These parts are held together by a steel bolt 7. Onto this may be turned grooves on either side for the location of securing spring washers 8. Another way of securing the lubricating roller halves to the steel bolt is as shown on the right in FIG. 11 and preferably consists of riveting of the steel bolt. The wear rings 9 and 9 control the rate of application of the solid lubricant by virtue of the fact,

that additional lubricant can only be worn off the lubricant roller halves at the rate at which the material at the circumference of the wear ring isworn away as the balls 3 roll over the wear ring. The material and the thickness of the ring are chosen such that at any time only as much lubricant is worn from the roller halves 1' and 1" as is absolutely necessary for the regeneration of the lubricant film on the ball and other rolling surfaces. Preferably the diameter H of the wear rings 9 is a few hundredths of a millimeter smaller than the diameter G of the front faces of the lubricating roller halves 1 and 1" in contact with the wear ring, thereby permitting an adequate supply of solid lubricant for the initial running in of the bearing.

In an example ball bearing according to the invention, the parts have the following dimensions,

Diameter 2A of the inner tracks (ball running tracks) of Ring 5 39.75 mm Ball diameter B 12.30 mm Diameter 2C around which center of ball travels 52.5 mm Outer diameter D of the lubricating rollers 1 and the metal rollers 2 10.06 mm Diameter 2E along and within which ball runs in the outer track ring 6 64.35 mm Diameter 2F along which the lubricating rollers 1 and the metal rollers 2 contact the outer track ring 6 62.25 mm Internal diameter G of the lubricating rollers and the metal rollers 8.00 mm The following relationships are obtained with respect to their relative movements:

When the outer track ring 6 is stationary and the inner track ring 5 rotates, and if the inner track rotates at a speed of n=l around the center of rotation M, the center points of the balls are moved by During pure rolling, the lubricating rollers 1 are rotated by n A/(A E) X 2F/D 2.35

If theoretically the axis of the lubricating rollers 1 were not movable but fixed at one radius, i.e., if the rollers could not roll around the outer track ring 6, the lubricating rollers 1 would when the inner track ring rotates at n=l around the center of rotation M rotate at Thus there is a difference in the relative rotational speed between the balls 3 and lubricating rollers l amounting to fi n n Inc speed of rotation of the inner track and removes a small amount from the solid lubricant reservoir off in the bearing material. The high Hertz pressures between ball and track produce lubricant plating onto both the surface of the ball and the running track, and are anchored to the latter in the depressions of the roughened surface. after a short period of operation of the bearing, an adhering, uniform thin film of lubricant is thus generated both on the surface of the ball and the running areas of the track rings, which cannot be wiped off, and which is particularly characterized by considerable temperature stability.

Each rolling element is preferably in contact with at least one lubricating spacer roller. This guarantees the direct transfer of the lubricant onto each rolling hearing element and each metallic spacer roller. The preferred version is for every other spacer roller to be of the lubricating type, when viewed along the circumference. Each antifriction bearing must have at least one pair of lubricating spacer rollers.

Part of the system for obtaining effective lubrication is the combination of solid lubricants known per se together with a fluorinated organic polymer in an organic binder such as epoxy resin. The basal planes of the solid lubricant particles are aligned relative to the surface of the rolling elements due to Hertz pressures which occur during operation. Particles of the fluorinated organic polymer are likewise embedded into this lubricating layer during rolling action. The particles also exhibit cold flow during rolling under high specific pressure. Thereby, an effect similar to a hydrodynamic lubrication is generated in such antifricti-on bearings built according to the invention.

For the lubricating spacer roller, a durable plastic material with at least percent at most 85 percent by weight of solid lubricant, 5 to 20 percent by weight of fluorinated organic polymer, 10 to percent by weight of an epoxy resin as well as, if desired, a cross- V linker and/or a catalyst for curing of the resin has been found suitable where a. the solid lubricant ingredients comprise one or severa] of the following component materials:

1. Sulphides, e.g., M08 W8 ZnS 2. Oxides, e.g., ZnO, PbO, SiO TiO ZrO 3. Selenides, e.g., MoSe WSe 5. Graphite M 6. Other fillers, e.g., boron nitride, asbestos, silicates. b. the fluorinated polymer is a polytetrafluorethylene wax or a fiuorinated ethylene-propylene-polymer, a preferred product being a PTF E wax having the following specification:

Bulk density: 600- 800 g/l Particle size: approx: T0 -30 pin Density: 2.25 2.29 g/cm Melting range: 324 to 327C.

Average molecular weight: 35,000 to 100,000;

c. The following types of epoxy resins can be used:

1. Reaction products of epichllorhydrine with bisphenol-A of the following general formula:

Oil:

where preferably N 7, and the epoxy equivalent weights are typically in the region of 200 to 900.

2. Novolac-resins with multi-epoxy functionality 3. Silicon-epoxy-copolymer-resins (as e.g., in US Pat. No. 2,288,710).

d. The crosslinkers or catalysts are selected from those types which are usually employed for the curing of epoxy resins, such as e.g., primary and secondary polyfunctional amines and their derivatives, polyamides, polycarboxylic acids and their anhydrides, tertiary amines, amine salts, BF complexes, and the like. Automatic presses employing the cold pressing technique are used to press the symmetrical bearing material components of the lubricating spacer rollers within close tolerances from granulated powders of the above mixture, the pressed components being thereafter subjected to a closely controlled heat treatment for obtaining the required hardness and wear resistance. By employing multiple tooling, the powder pressing process know per se permits economical mass production of the bearing material components of the lubricating spacer rollers, thus making them economically attractive parts for anti-friction bearings.

The following are some examples for the composition of lubricating bearing materials according to the inventron:

EXAMPLE 1 EXAMPLE 2 Composition in weight percent.

19.6 percent molybdenum disulphide 19.6 percent zinc sulphide 14.4 percent Lubricating graphite 14.4 calcium fluoride, of the synthetic, precipitated type 16.7 percent epoxy resin 3.3 percent 1,2,3,4-cyclopentanetetracarboxylic acid dianhydride 10 percent polytetrafluorethylene wax 2 percent zinc oxide Specification of materials as in Example 1.

EXAMPLE 3 Composition in weight percent. 23.9 percent molybdenum disulphide 17.9 percent zinc oxide 14.5 percent calcium fluoride 14.5 percent graphite 16 percent epoxy resin 3.2 percent 1,2,3,4-cyclopentanetetracarboxylic acid 65 dianhydride 10 percent polytetrafluorethylene wax Specification of materials as in Example 2.

The invention is further illustrated with reference to the following experiments:

EXPERIMENT NO. 1

A ball bearing No. 6306 comprising seven lubricating spacer rollers according to FIG. 2 and a divided lubricating spacer roller without wear ring 9 according to FIG. 3 was tested at an ambient temperature of 22C. under the following conditions:

Max. radial bearing load p 600 kilogram force Axial load P zero Speed n 200 rpm (constant during duration of experiment) Duration of test 104 hours (experiment then discontinued with no bearing failure) The result is shown in the following Table I:

TABLE I Bearing load After in kilograms Coefficient of Temperature of hours force friction bearing in C. 1 25 0.0094 24 1 1.5 000 0.0066 40 17.5 600 0.0053 37 32 600 0.0057 35 56 600 0.0053 35 600 0.0053 33.5 7| 600 0.0053 32 92 600 0.0050 30 104 600 0.0048 29 EXPERIMENT NO. 2

As a comparison with present day practice a standard ball bearing No. 6306 with a normal radial play and a lubricant filling consisting of 20 g Lithium grease (Shell Alvania 2) was tested under identical loading intervals and conditions and at the same ambient temperature of 22C. as the bearing tested in Experiment No. l with the results shown in the following Table II:

TABLE II Bearing load After in kilogram Coefficient of Temperature of hours force friction bearing in C. 1 25 0.031 30 11.5 600 0.0050 35 17.5 600 0.0053 38 32 600 0.0054 38 56 600 0.0055 40 65 600 0.0052 40 71 600 0.0054 40 On comparison between Experiments No. l and No. 2 it can be seen that an identical coefficient of friction of p. =0.0050 is established after 17.5 hours and remains constant until the end of the experiments. What is most surprising is, that a dry ball bearing exhibits the same low coefficient of friction as one lubricated with grease. The temperature in Experiment No. I initially running, while in Experiment No. 2 a steady rise to 40C. took place. This rise in temperature can be explained by the steady kneading action of the grease in conventional bearings; moreover temperature does not stay constant at 40C., but continues to rise steadily and slowly, therefore this invention gives rise to larger benefits over longer periods of operation.

In FIGS. 6, 7 and 8 a self-lubricating roller bearing according to the invention is shown in which are fitted lubricating spacer rollers l l and metal spacer rollers 12 to act as movable spacers for the steel bearing rollers. The spacer rollers are fitted with flanges 21 and 22 at their front faces with which they roll along the inside of the outer track ring. Apart from the fact, that instead of balls as shown in the embodiment according to FIGS. 1 to 5, bearing rollers 13 are used in the last mentioned embodiment shown in FIGS. 6, 7 and 8 and therefore the spacer rollers 11 and 12 have cylindrical rolling faces, the interrelationships as regards motion as well as their effect are the same as in the ball bearings. Therefore the same reference letters and numerals for functionally similarly acting parts of the roller bearing are employed as have been used for the ball bearing.

In the FIGS. 9 to 14 parts of a self-lubricating ball bearing are shown, which are similar to the bearing shown in FIGS. 1 to 5. This drawing incorporates the dimensions which are important for a practical execution of the invention. For like parts the same reference letters and numerals are used as for the corresponding parts in the embodiment according to FIGS. 1 to 5. FIG. 15 clearly shows the comparison of results using this invention with results using grease lubricated bearings of the prior art. The relationship of the coefficient of friction to the time of testing in hours is determined by means of the well known Lubrimeter. The plot of experimental data in FIG. 15 shows graphically the results of the afore described data summarized in Table I and II above in connection with Experiments Nos. 1 and 2. The thick line illustrates the coefficient of friction vs. time relationship in Experiment No. 1 while the thin line shows for comparative purposes the results of Experiment No. 2.

Obviously other variations and modifications of the invention will become obvious to those skilled in the art from a reading of the foregoing descriptions of preferred embodiments. It is to be understood therefore that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

That which is claimed is:

l. A self-lubricating antifriction bearing comprising rolling bearing elements located between two annular tracks, which bearing elements are separated by spacer elements in the form of spacer rollers each in contact with two adjacent rolling bearing elements and at least one of said spacer rollers being a lubricating roller made from a lubricating bearing material, characterized in that each lubricating roller is axially subdivided into a number of generally cylindrical sections in the region in which it rolls over the rolling bearing element and the surface of the outer track annulus, of which at least one section is made from a. material of greater wear resistance than that of the lubricating bearing material.

2. An anti-friction bearing as defined in claim 1, characterized in that each lubricating roller is fitted with metal wear rings in the center and at the two end faces, and held together with the lubricating sections by a steel bolt so as to form a composite lubricating roll. 

2. An anti-friction bearing as defined in claim 1, characterized in that each lubricating roller is fitted with metal wear rings in the center and at the two end faces, and held together with the lubricating sections by a steel bolt so as to form a composite lubricating roll. 